Commercial unsaturated polyester resins are prepared by reacting glycols and unsaturated dicarboxylic acids or their derivatives to give liquid polymers of intermediate molecular weight. For example, propylene glycol reacts with maleic anhydride to give an unsaturated polyester resin. Unsaturated polyester resins react with vinyl monomers such as styrene in the presence of radical initiators to give cured, crosslinked solids of high strength.
Saturated polyester polyols are made by reacting glycols with saturated dicarboxylic acids or their derivatives. Saturated polyester polyols are often used for polyurethanes. In spite of the usefulness of both saturated polyester polyols and unsaturated polyester resins, no one has previously taught how to make polyesters from polyethers.
Conversion of a polyether to a polyester requires an initial ether-cleavage reaction. Ether cleavage typically requires harsh reagents such as concentrated sulfuric acid and hydriodic acid, and is generally not commercially attractive. Ganum and Small (J. Org. Chem. 39 (1974) 3728) showed that aliphatic ethers react under relatively mild conditions with acetic anhydride and ferric chloride to give esters. Ether -cleavage reactions have apparently not been used to make polyesters from polyethers.
Polyether polyols recovered from polyurethane foams, elastomers, and the like, are a convenient source of polyethers. How best to convert these materials to useful products is still unclear. If recovered polyethers, especially polyether polyols, could be converted practically to other useful polymers, more people could recycle and polyurethanes. Unfortunately polyethers recovered from polyurethanes typically come from many different sources, and are usually complex mixtures. The key is in finding a way to make something useful from the complex polyether mixture.
Polyether polyols give flexibility to polyurethanes. Often, polyurethanes with greater stiffness and strength would be desirable. Cured polyesters are strong and tough, but can often be too stiff or brittle. A desirable product would combine the flexibility advantages of polyurethanes with the toughness and strength of cured polyesters. Such a unique product might be made if only one could find a way to selectively introduce unsaturated polyester linkages into a polyether backbone.